Photosensitive resin compositions and photosensitive elements obtained by laminating them onto support films and covering them with protective films are widely used as resist materials for etching, plating, and the like in the field of printed circuit board manufacturing.
The following method is ordinarily employed for manufacture of printed circuit boards. Specifically, the photosensitive resin composition is laminated on a circuit-forming board (copper board, etc.) and active light rays are irradiated on prescribed areas of the photosensitive resin composition (pattern exposure) for photocuring of the exposed sections, and then the uncured sections are removed with a developing solution (development) to form a resist pattern. The resist pattern-formed board is then subjected to etching or plating to form a pattern, and then the cured sections (resist pattern) are released from the board.
Removal of the uncured sections is usually accomplished using an aqueous alkali solution as the developing solution. The aqueous alkali solution may be, for example, a 0.1-5 wt % sodium carbonate dilute solution or a 0.1-5 wt % potassium carbonate dilute solution. The main purpose of the developing treatment is dissolution removal of the uncured sections, but the cured sections may also swell, while not dissolving, in the developing solution. Such swelling of the cured sections produces poor adhesion or line width bloating of the resist pattern, and has constituted a major cause of reduced resolution. In order to improve the resolution, therefore, it is effective to design a photosensitive resin composition which can form cured sections resistant to swelling in aqueous alkali solutions.
On the other hand, the cured sections (resist pattern) are released with a stronger alkali aqueous solution than the aqueous alkali solution used for development. As strong alkali aqueous solutions there are used, for example, 1-10 wt % aqueous sodium hydroxide or 1-10 wt % aqueous potassium hydroxide. The principle for removal of the cured sections is based on stress produced by swelling, and reduced adhesion with the board. In order to improve the removability of the cured sections, therefore, it is effective to design a photosensitive resin composition which can form cured sections which easily swell in aqueous alkali solutions.
In other words, there is a trade-off between resolution and removability, and consequently it has been difficult to achieve a high level of both qualities. In particular, it has been difficult to obtain photosensitive resin compositions with excellent resolution capable of forming resist patterns with space widths and line widths of 20 μm and smaller, while also allowing reliable removal of the resist pattern.
Incidentally, many constituent materials for photosensitive resins compositions have been studied in recent years, and for example, there have been proposed photocrosslinking polymers that can be resolubilized by heating, and compositions for forming them (see Non-patent document 1). Also known in the field of thermosetting resins are crosslinking polymers having such properties as to dissociate upon external stimuli such as heat, and compositions for forming them (see Non-patent document 2).
Non-patent document 1: Shiroi, M. “Mirai Zairyo”, Vol. 2, No. 9, p. 20-25, 2002
Non-patent document 2: Otsuka, H. “Kobunshi Gakkai Yokoshu”, Vol. 48, No. 8, p. 1635-1636, 1999